The unveiling took place in the final few seconds of the season 8 finale, as Milioti's yet-unnamed character simply walked up to a Long Island Rail Road ticket booth to purchase one ticket to the fictional Farhampton, presumably to go play in the band at the impending nuptials between Barney (Neil Patrick Harris) and Robin (Cobie Smulders). The show didn't exactly spell out the reveal (casual fans could have missed it), but there was one key to knowing the doe-eyed girl was the mother: the bright yellow umbrella she was holding. That's the linchpin accessory the show's narrator and father Ted (Josh Radnor) previously set up as the woman's signature — and identifying — item.

EW was on set for the filming of the game-changing scene, and scored an exclusive interview with co-creators Carter Bays and Craig Thomas. The pair revealed, among many other things, that we likely would have met the mother in May 2013 no matter what: The original plan was for the show to end after just eight seasons (meaning it would have been over...now), with the mother briefly introduced in the series finale. Only after HIMYM was extended to nine seasons did Bays and Thomas make the decision to reveal the mother before the final season — in tonight's episode. (Though it seems Ted won't be coming face-to-face with her until much later next season.)

While the scene answered the biggest burning question — who was the woman at the center of the saga that Ted has been reliving for his kids (and viewers) since the show first launched in 2005? — it left us with many, many more: Why do this now? Why didn't they cast a big, big star? Why wasn't the mother actually Robin? How was the long-awaited casting kept secret from the show's incredibly rabid followers? Read on as Bays and Thomas break down the Mother of all reveals.

Entertainment Weekly: It's already been announced that next season will be your last. With another year to go, why introduce the mother now?

Carter Bays: One of our hard and fast rules [when we thought we were doing eight seasons] was that we didn't want to meet her until the very end. We felt like, now that we're doing another year, let's find an interesting new twist.

Craig Thomas: We've talked here and there about letting the audience see the mother before Ted. Would that be fascinating or let some air out of the balloon? We were scared of it for a long time, but this past season, it came up, and it just fit in so well. Ultimately we view it like we've been honing in on this mother mystery for so long. In season one, it was like a shot of planet earth from outer space. And we've honed in and honed in and honed in, and we look at season nine as like now we're down to Google street view. We've gone from a super-wide shot to super-microscopic-tight, and it just felt right to see the mother's face and to give the audience that gift and that knowledge. There was something exciting about getting a little bit of her before Ted ever does. There was something that we felt like this audience who has stuck with us for all of these years we wanted to reward them with that.

Bays: And to give ourselves the gift of having something. We didn't want to do season 9 unless we had something that just got us really excited to write it. This concept got us very excited to write it and lent itself to a lot of great ideas that came out. The tipping point was when you have enough ideas that you're going to be bummed if you don't get to try these ideas, that's when it became worth it for us to do season 9, and part of that is revealing the mother. The idea of getting to know her, getting to know where she's coming from, it became too tantalizing to pass up. We always liked the poetic ending of you never really get to know her, you just see her face or something.

EW: Truly, this is pay-off for the fans.

Thomas: The thing we're proud about in this series, we were able to pack some real surprises into the conventional sitcom form. A lot of viewers have given up on meeting the mother prior to the final episode. There are a lot of people who think that's true. I think this will count as a genuine surprise for a lot of people. A lot of people think, "Oh, they got another year; we're never going to see her face this year." I think the way that the season ends, I'm hoping it will blow some people's minds and surprise them and make them want to tune in and see what the hell we're going to do with that.

EW: There wasn't a peep out there about this happening. Was the surprise element crucial to how you wanted this to roll out on screen?

Bays: It's an intended thing. And partly, it's a fun way to do it. It will be fun to see people's reactions. There's something about as far as how as our experience as the audience is reflected in Ted's experience as a single guy, I like the idea of you never know when it's going to happen, and when it does happen, it just happens and there she is. I think it's a way to put the audience in Ted's shoes a little bit even though he doesn't actually meet her in this episode.

EW: How did you keep the whole thing a secret?

Thomas: In the script we called the character "definitely not the mother," so it was very good code. We got very CIA and intense about it: We really didn't put it on paper; we never emailed the outline or the script. We literally just kept it on hard copies of paper that we messengered back and forth to people and then got the copies back and destroyed [them].

Bays: We had like a whole fake title. The script that we auditioned her from was titled "USC Student Thesis Film."

Thomas: Something no one in Hollywood would ever actually read.

Bays: All the extras from the scene with the mother are staff from How I Met Your Mother. They're all there. It was really fun.

EW: How did it feel to finally have Milioti on set and see it all play out?

Thomas: She just had to walk and say one line, but we were all freaking out and losing our minds. All she said was, "One ticket to Far Hampton, please." It was a very surreal moment. It was a moment we pictured for a lot of years, and ultimately it was great.

EW: It seems like people thought the mother would be a big star. Did you ever consider going that route?

Thomas: We didn't want it to be a big famous star because we didn't want the wider audience to have associations with whatever actress this would be, where it's like, "Oh, it's Anne Hathaway and I think blank of Anne Hathaway...." You're waiting years to meet this woman, and it's like, "Oh, he's in love with Amy Adams just like the rest of America is." The whole idea is that Ted's never seen this woman before, so it better feel that way to the audience." Cristin Milioti is she's a fantastic actress and she's been in [Broadway musica] Once, and it's a Tony-nominated, wonderful musical but she hasn't done a ton of big TV parts or bigger film parts. It seems so much more interesting and so much more ted to find someone special and unique and new, someone that we haven't seen before and the whole idea is that Ted's never seen this woman before, so it better feel that way to the audience.

Bays: I don't think it ever occurred to us. Honestly, exhibit A for us in the discussions was Cobie Smulders. In the pilot of our show, Ted sees [Cobie Smulders'] Robin for the first time and — without naming names — the part of Robin was offered to a pretty famous actress and she turned it down and then we ended up going with Cobie, who was our first choice from the beginning. Thank God we did for a million reasons but among those is the fact that when Ted's seeing her for the first time, America's seeing her for the first time — the intriguingness of that propelled the show going forward and kept the show alive.

EW: Was there ever a moment when you thought about trying to make Robin the mother?

Bays: No. We've heard that question a lot. What always made the show interesting to us is that Ted meets the perfect woman, and it's [still] not his final love story.

For more How I Met Your Mother's big reveal — as well as exclusive details about what fans can expect to happen in the show's ninth and final season -- pick up a copy of this week's Entertainment Weekly, available on newsstands May 17.